The present invention is related to the production of galloid organics and more specifically to methods of producing gallic acid and pyrogallol from bioconversion of a carbon source.
Among a spectrum of uses, gallic acid and pyrogallol are often incorporated into chemical syntheses to provide the trihydroxylated aromatic ring of biologically-active molecules such as the antibiotic trimethoprim 1, the coronary vasodilator trimetazidine 2, the insecticide bendiocarb 3, and the muscle relaxant gallamine triethiodide 4. The current commercial sources 
of gallic acid include gall nuts, an insect carapace harvested in China, and tara powder, an isolate derived from the ground seed pod of a tree found in Peru (Leston, G. In Kirk-Othmer Encyclopedia of Chemical Technology; Kroschwitz, J. I.; Howe-Grant, M., Ed.; Wiley: New York (1996), Vol. 19, p. 778). Pyrogallol is currently synthesized by thermal decarboxylation of gallic acid in copper autoclaves (Leston, G. In Kirk-Othmer Encyclopedia of Chemical Technology; Kroschwitz, J. I.; Howe-Grant, M., Ed.; Wiley: New York (1996), Vol. 19, p. 778).
Because of the continuing uncertainties of supplies of gall nuts and tara powder, which are used for gallic acid and pyrogallol manufacture, there is interest in the development of synthetic processes. Various approaches were investigated in the synthesis of pyrogallol from readily available petrochemicals. The first synthetic pyrogallol that was industrially manufactured used basic hydrolysis of 2,2,6,6-tetrachlorocyclohexanone (German Patent No. 2,653,446). The preparation of the starting material by chlorination of cyclohexanone in the presence of collidine as the catalyst has been patented (British Patent No. 1,258,700). Cyclohexanone""s main commercial synthesis begins with benzene, a petroleum-derived chemical with known toxic and carcinogenic activity. Other synthetic approaches involve hydroxylation of resorcinol with 50% H2O2 in the presence of hexafluoroacetone at 60xc2x0 C. to give a mixture of pyrogallol and 1,2,4-trihydroxybenzene (Japan Patent No. 75151832), or hydrolysis of 2,6-dimethoxyphenol using 48% hydrobromic acid (U.S. Pat. No. 4,172,960). The 2,6-dimethoxyphenol is produced by reaction of 2,6-dibromophenol with sodium methoxide.
Therefore, it would be desirable to provide methods for obtaining large quantities of gallic acid and pyrogallol that did not require the isolation of natural products from non-row crops. It would also be desirable if the methods were cost-efficient using inexpensive starting materials. Furthermore, such methods should be simple and environmentally benign.
A bioengineered synthesis scheme for production of gallic acid from a carbon source is provided. In one embodiment, the bioconversion methods of the present invention comprise the microbe-catalyzed conversion of a carbon source to gallic acid. As shown in the synthesis scheme of FIG. 1, the microbe-catalyzed conversion of the present invention requires five enzymes which may be provided by a recombinant microbe. In a preferred embodiment, the recombinant microbe is Escherichia coli designed to cause the two-step conversion of 3-dehydroshikimic acid to gallic acid.
A bioengineered scheme for the production of pyrogallol from gallic acid is also provided. In one embodiment, the bioconversion methods of the present invention comprise the microbe-catalyzed conversion of gallic acid to pyrogallol. As shown in the synthesis scheme of FIG. 1, the microbe-catalyzed conversion step requires one enzyme which may be provided by a recombinant microbe. In a preferred embodiment, the recombinant microbe is Escherichia coli designed to cause the decarboxylation of gallic acid to pyrogallol.
The biocatalytic synthesis methods for gallic acid and pyrogallol provided herein are believed to be environmentally benign, economically attractive, and utilize abundant renewable sources as a starting materials.
Additional objects, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.